A standard shower head has a body forming a pressurizable compartment one wall of which is formed with an array of throughgoing perforations. When the compartment is pressurized, respective streams of water emerge from the perforations.
These perforations are of fairly small diameter, at most a few millimeters, and the outer or downstream face of the perforated wall is exposed to the atmosphere. Thus any water on the outer face will dry and, if it is rich in calcium, will leave lime deposits behind, in particular at the edges of the flow perforations.
German patent document 3,107,808 filed 28 February 1981 by Fritz Wagner describes a shower head having a lining formed with a plurality of elastomeric nipples that project through the flow holes. These nipples normally collapse and are closed, but when the head is pressurized they open up to emit respective streams of water. Thus any lime formations will be minimal, and will normally be flushed away due both to the erosion of the water stream acting on them and the poor hold on the elastomeric material. Such an arrangement is fairly complicated and the spray produced by it is highly variable with pressure.
Another shower head is described in German patent document 3,044,310 filed 25 November 1980 by Willy Orszullok. It has a liner With a plurality of nipples which, unlike the above-described Wagner system, do not close when unpressurized but which extend through respective holes in a guide plate. This plate can be shifted to direct the sprays emerging from the nipples. There is no significant lime-removing system here.